Cooling system for a computer system

ABSTRACT

A cooling system for a computer system comprises at least one unit such as a central processing unit (CPU) generating thermal energy and a reservoir having an amount of cooling liquid, said cooling liquid intended for accumulating and transferring of thermal energy dissipated from the processing unit to the cooling liquid. The cooling system has a heat exchanging interface for providing thermal contact between the processing unit and the cooling liquid for dissipating heat from the processing unit to the cooling liquid. Different embodiments of the heat exchanging system as well as means for establishing and controlling a flow of cooling liquid and a cooling strategy constitutes the invention of the cooling system.

This is a continuation application of application Ser. No. 15/991,375,filed May 29, 2018, which is a continuation of application Ser. No.15/626,393, filed Jun. 19, 2017 (issued on Sep. 18, 2018 as U.S. Pat.No. 10,078,354 B2), which is a continuation of Ser. No. 15/347,938,filed Nov. 10, 2016 (issued on Jul. 25, 2017 as U.S. Pat. No. 9,715,260B2), which is a continuation application of application Ser. No.13/942,922, filed Jul. 16, 2013, which is a continuation application ofapplication Ser. No. 13/547,240, filed Jul. 12, 2012, which is acontinuation application of application Ser. No. 12/826,768, filed Jun.30, 2010 (issued on Aug. 14, 2012 as U.S. Pat. No. 8,240,362 B2), whichis a divisional of application Ser. No. 10/578,578, filed May 5, 2006(issued on Jul. 5, 2011 as U.S. Pat. No. 7,971,632 B2), which is a U.S.national phase application of PCT/DK2004/000775, filed on Nov. 8, 2004.These applications are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

The present invention relates to a cooling system for a centralprocessing unit (CPU) or other processing unit of a computer system.More specifically, the invention relates to a liquid-cooling system fora mainstream computer system such as a PC.

During operation of a computer, the heat created inside the CPU or otherprocessing unit must be carried away fast and efficiently, keeping thetemperature within the design range specified by the manufacturer. As anexample of cooling systems, various CPU cooling methods exist and themost used CPU cooling method to date has been an air-coolingarrangement, wherein a heat sink in thermal contact with the CPUtransports the heat away from the CPU and as an option a fan mounted ontop of the heat sink functions as an air fan for removing the heat fromthe heat sink by blowing air through segments of the heat sink. Thisair-cooling arrangement is sufficient as long as the heat produced bythe CPU is kept at today's level, however it becomes less useful infuture cooling arrangements when considering the development of CPUssince the speed of a CPU is said to double perhaps every 18 months, thusincreasing the heat production accordingly.

Another design used today is a CPU cooling arrangement where coolingliquid is used to cool the CPU by circulating a cooling liquid inside aclosed system by means of a pumping unit, and where the closed systemalso comprises a heat exchanger past which the cooling liquid iscirculated.

A liquid-cooling arrangement is more efficient than an air-coolingarrangement and tends to lower the noise level of the coolingarrangement in general. However, the liquid-cooling design consists ofmany components, which increases the total installation time, thusmaking it less desirable as a mainstream solution. With a trend ofproducing smaller and more compact PCs for the end-users, the greateramount of components in a typical liquid-cooling arrangement is alsoundesirable. Furthermore, the many components having to be coupledtogether incurs a risk of leakage of cooling liquid from the system.

SUMMARY OF INVENTION

It may be one object of the invention to provide a small and compactliquid-cooling solution, which is more efficient than existingair-cooling arrangements and which can be produced at a low costenabling high production volumes. It may be another object to create aliquid-cooling arrangement, which is easy-to-use and implement, andwhich requires a low level of maintenance or no maintenance at all. Itmay be still another object of the present invention to create aliquid-cooling arrangement, which can be used with existing CPU types,and which can be used in existing computer systems.

This object may be obtained by a cooling system for a computer system,said computer system comprising: at least one unit such as a centralprocessing unit (CPU) generating thermal energy and said cooling systemintended for cooling the at least one processing unit, a reservoirhaving an amount of cooling liquid, said cooling liquid intended foraccumulating and transferring of thermal energy dissipated from theprocessing unit to the cooling liquid, a heat exchanging interface forproviding thermal contact between the processing unit and the coolingliquid for dissipating heat from the processing unit to the coolingliquid, a pump being provided as part of an integrate element, saidintegrate element comprising the heat exchanging interface, thereservoir and the pump, said pump intended for pumping the coolingliquid into the reservoir, through the reservoir and from the reservoirto a heat radiating means,—said heat radiating means intended forradiating thermal energy from the cooling liquid, dissipated to thecooling liquid, to surroundings of the heat radiating means.

By providing an integrate element, it is possible to limit the number ofseparate elements of the system. However, there is actually no need forlimiting the number of elements, because often there is enough spacewithin a cabinet of a computer system to encompass the differentindividual elements of the cooling system. Thus, it is surprisinglythat, at all, any attempt is conducted of integrating some of theelements.

In preferred embodiments according to this aspect of the invention, thepump is placed inside the reservoir with at least an inlet or an outletleading to the liquid in the reservoir. In an alternative embodiment thepump is placed outside the reservoir in the immediate vicinity of thereservoir and wherein at least an inlet or an outlet is leading directlyto the liquid in the reservoir. By placing the pump inside the reservoiror in the immediate vicinity outside the reservoir, the integrity of thecombined reservoir, heat exchanger and pump is obtained, so that theelement is easy to employ in new and existing computer systems,especially mainstream computer systems.

The object may also be obtained by a cooling system for a computersystem, said computer system comprising: at least one unit such as acentral processing unit (CPU) generating thermal energy and said coolingsystem intended for cooling the at least one processing unit, areservoir having an amount of cooling liquid, said cooling liquidintended for accumulating and transferring of thermal energy dissipatedfrom the processing unit to the cooling liquid, a heat exchanginginterface for providing thermal contact between the processing unit andthe cooling liquid for dissipating heat from the processing unit to thecooling liquid, a pump intended for pumping the cooling liquid into thereservoir, through the reservoir and from the reservoir to a heatradiating means, said cooling system being intended for thermal contactwith the processing unit by means of existing fastening means associatedwith the processing unit, and said heat radiating means intended forradiating from the cooling liquid thermal energy, dissipated to thecooling liquid, to surroundings of the heat radiating means.

The use of existing fastening means has the advantage that fitting ofthe cooling system is fast and easy. However, once again there is noproblem for the person skilled in the art to adopt specially adaptedmounting means for any element of the cooling system, because there arenumerous possibilities in existing cabinets of computer systems formounting any kind of any number of elements, also elements of a coolingsystem.

In preferred embodiments according to this aspect of the invention, theexisting fastening means are means intended for attaching a heat sink tothe processing unit, or the existing fastening means are means intendedfor attaching a cooling fan to the processing unit, or the existingfastening means are means intended for attaching a heat sink togetherwith a cooling fan to the processing unit. Existing fastening means ofthe kind mentioned is commonly used for air cooling of CPUs of computersystems, however, air cooling arrangements being much less complex thanliquid cooling systems. Nevertheless, it has ingeniously been possibleto develop a complex and effective liquid cooling system capable ofutilising such existing fastening means for simple and less effectiveair cooling arrangements.

According to an aspect of the invention, the pump is selected from thefollowing types: Bellows pump, centrifugal pump, diaphragm pump, drumpump, flexible liner pump, flexible impeller pump, gear pump,peristaltic tubing pump, piston pump, processing cavity pump, pressurewasher pump, rotary lobe pump, rotary vane pump and electro-kineticpump. By adopting one or more of the solution of the present invention,a wide variety of pumps may be used without departing from the scope ofthe invention.

According to another aspect of the invention, driving means for drivingthe pump is selected among the following driving means: electricallyoperated rotary motor, piezo-electrically operated motor, permanentmagnet operated motor, fluid-operated motor, capacitor-operated motor.As is the case when selecting the pump to pump the liquid, by adoptingone or more of the solution of the present invention, a wide variety ofpumps may be used without departing from the scope of the invention.

The object may also be obtained by a cooling system for a computersystem, said computer system comprising: at least one unit such as acentral processing unit (CPU) generating thermal energy and said coolingsystem intended for cooling the at least one processing unit, areservoir having an amount of cooling liquid, said cooling liquidintended for accumulating and transferring of thermal energy dissipatedfrom the processing unit to the cooling liquid, a heat exchanginginterface for providing thermal contact between the processing unit andthe cooling liquid for dissipating heat from the processing unit to thecooling liquid, a pump intended for pumping the cooling liquid into thereservoir, through the reservoir and from the reservoir to a heatradiating means, and said cooling system further comprising a pumpwherein the pump is driven by an AC electrical motor by a DC electricalpower supply of the computer system, where at least part of theelectrical power from said power supply is intended for being convertedto AC being supplied to the electrical motor.

It may be advantageous to use an AC motor, such as a 12V AC motor, fordriving the pump in order to obtain a stabile unit perhaps having tooperate 24 hours a day, 365 days a year. However, the person skilled inthe art will find it unnecessary to adopt as example a 12V motor becausehigh voltage such as 220V or 110V is readily accessible as this is theelectrical voltage used to power the voltage supply of the computersystem itself. Although choosing to use a 12V motor for the pump, it hasnever been and will never be the choice of the person skilled in the artto use an AC motor. The voltage supplied by the voltage supply of thecomputer system itself is DC, thus this will be the type of voltagechosen by the skilled person. In preferred embodiments according to anyaspect of the invention, an electrical motor is intended both fordriving the pump for pumping the liquid and for driving the a fan forestablishing a flow of air in the vicinity of the reservoir, or anelectrical motor is intended both for driving the pump for pumping theliquid and for driving the a fan for establishing a flow of air in thevicinity of the heat radiating means, or an electrical motor is intendedboth for driving the pump for pumping the liquid, and for driving the afan for establishing a flow of air in the vicinity of the reservoir, andfor driving the a fan for establishing a flow of air in the vicinity ofthe heat radiating means.

By utilising a single electrical motor for driving more than one elementof the cooling system according to any of the aspects of the invention,the lesser complexity and the reliability of the cooling system will befurther enhanced.

The heat exchanging interface may be an element being separate from thereservoir, and where the heat exchanging interface is secured to thereservoir in a manner so that the heat exchanging interface constitutespart of the reservoir when being secured to the reservoir.Alternatively, the heat exchanging interface constitutes an integratesurface of the reservoir, and where the heat exchanging surface extendsalong an area of the surface of the reservoir, said area of surfacebeing intended for facing the processing unit and said area of surfacebeing intended for the close thermal contact with the processing unit.Even alternatively, the heat exchanging interface is constitutes by afree surface of the processing unit, and where the free surface iscapable of establishing heat dissipation between the processing unit andthe cooling liquid through an aperture provided in the reservoir, andwhere the aperture extends along an area of the surface of thereservoir, said surface being intended for facing the processing unit.

The object may also be obtained by a cooling system for a computersystem, said computer system comprising: at least one unit such as acentral processing unit (CPU) generating thermal energy and said coolingsystem intended for cooling the at least one processing unit comprising,a reservoir having an amount of cooling liquid, said cooling liquidintended for accumulating and transferring of thermal energy dissipatedfrom the processing unit to the cooling liquid, a heat exchanginginterface for providing thermal contact between the processing unit andthe cooling liquid for dissipating heat from the processing unit to thecooling liquid, a pumping means being intended for pumping the coolingliquid into the reservoir, through the reservoir and from the reservoirto a heat radiating means, said heat radiating means intended forradiating thermal energy from the cooling liquid, dissipated to thecooling liquid, to surroundings of the heat radiating means, said heatexchanging interface constituting a heat exchanging surface beingmanufactured from a material suitable for heat conducting, and with afirst side of the heat exchanging surface facing the central processingunit being substantially plane and with a second side of the heatexchanging surface facing the cooling liquid being substantially planeand said reservoir being manufactured from plastic, and channels orsegments being provided in the reservoir for establishing a certainflow-path for the cooling liquid through the reservoir.

Providing a plane heat exchanging surface, both the first, inner sideand on the second, outer side, results in the costs for manufacturingthe heat exchanging surface is reduced to an absolute minimum. However,a plane first, inner surface may also result in the cooling liquidpassing the heat exchanging surface too fast. This may be remedied byproviding grooves along the inner surface, thereby providing a flow pathin the heat exchanging surface. This however results in the costs formanufacturing the heat exchanging surface increasing. The solution tothis problem according to the invention has been dealt with by providingchannels or segments in the reservoir housing instead. The reservoirhousing may be manufactured by injection moulding or by casting,depending on the material which the reservoir housing is made from.Proving channels or segments during moulding or casting of the reservoirhousing is much more cost-effective than milling grooves along the innersurface of the heat exchanging surface.

The object may also be obtained by a cooling system for a computersystem, said computer system comprising: at least one unit such as acentral processing unit (CPU) generating thermal energy and said coolingsystem intended for cooling the at least one processing unit comprising,at least one liquid reservoir mainly for dissipating or radiating heat,said heat being accumulated and transferred by said cooling liquid, saidcooling system being adapted such as to provide transfer of said heatfrom a heat dissipating surface to a heat radiating surface where saidat least one liquid reservoir being provided with one aperture intendedfor being closed by placing said aperture covering part of,alternatively covering the whole of, the at least one processing unit insuch a way that a free surface of the processing unit is in direct heatexchanging contact with an interior of the reservoir, and thus in directheat exchanging contact with the cooling liquid in the reservoir,through the aperture.

Heat dissipation from the processing unit to the cooling liquid must bevery efficient to ensure proper cooling of the processing unit,Especially in the case, where the processing unit is a CPU, the surfacefor heat dissipation is limited by the surface area of the CPU. This maybe remedied by utilising a heat exchanging surface being made of amaterial having a high thermal conductivity such as copper or aluminiumand ensuring a proper thermal bondage between the heat exchangingsurface and the CPU.

However, in a possible embodiment according to the features in the aboveparagraph, the heat dissipation takes place directly between theprocessing unit and the cooling liquid by providing an aperture in thereservoir housing, said aperture being adapted for taking up a freesurface of the processing unit. Thereby, the free surface of theprocessing unit extends into the reservoir or constitutes a part of theboundaries of the reservoir, and the cooling liquid has direct access tothe free surface of the processing unit.

According to one aspect of the invention, a method is envisaged, saidmethod of cooling a computer system comprising at least one unit such asa central processing unit (CPU) generating thermal energy and saidmethod utilising a cooling system for cooling the at least oneprocessing unit and, said cooling system comprising a reservoir, atleast one heat exchanging interface, an air blowing fan, a pumpingmeans, said method of cooling comprising the steps of applying one ofthe following possibilities of how to operate the computer system:establishing, or defining, or selecting an operative status of thecomputer system, controlling the operation of at least one of thefollowing means of the computer system; the pumping means and the airblowing fan in response to at least one of the following parameters; asurface temperature of the heat generating processing unit, an internaltemperature of the heat generating processing unit, or a processing loadof the CPU and in accordance with the operative status beingestablished, defined or selected, controlling the operation of thecomputer system in order to achieve at least one of the followingconditions; a certain cooling performance of the cooling system, acertain electrical consumption of the cooling system, a certain noiselevel of the cooling system.

Applying the above method ensures an operation of the computer systembeing in accordance with selected properties during the use of thecomputer system. For some applications, the cooling performance is vitalsuch as may be the case when working with image files or whendownloading large files from a network during which the processing unitsis highly loaded and thus generating much heat. For other applications,the electrical power consumption is more vital such as may be the casewhen utilising domestic computer systems or in large office building inenvironments where the electrical grid may be weak such as in thirdcountries. In still other applications, the noise generated by thecooling system is to be reduced to a certain level, which may be thecase in office buildings with white collar people working alone, or athome, if the domestic computer perhaps is situated in the living room,or at any other location where other exterior considerations have to bedealt with.

According to another aspect of the invention, a method is envisaged,said method being employed with cooling system further comprising apumping means with an impeller for pumping the cooling liquid through apumping housing, said pumping means being driven by an AC electricalmotor with a stator and a rotor, and said pumping means being providedwith a means for sensing a position of the rotor, and wherein the methodcomprises the following steps: initially establishing a preferredrotational direction of the rotor of the electrical motor, before startof the electrical motor, sensing the angular position of the rotor,during start, applying an electrical AC voltage to the electrical motorand selecting the signal value, positive or negative, of the AC voltageat start of the electrical motor, said selection being made according tothe preferred rotational direction, and said application of the ACvoltage being performed by the computer system for applying the ACvoltage from the electrical power supply of the computer system duringconversions of the electrical DC voltage of the power supply to ACvoltage for the electrical motor.

Adopting the above method according to the invention ensures the mostefficient circulation of cooling liquid in the cooling system and at thesame time ensures the lowest possible energy consumption of theelectrical motor driving the impeller. The efficient circulation of thecooling liquid is obtained by means of an impeller being designed forrotation in one rotational direction only, thus optimising the impellerdesign with regard to the only one rotational direction as opposed toboth rotational directions. The low energy consumption is achievedbecause of the impeller design being optimised, thus limiting thenecessary rotational speed of the impeller for obtaining e certainamount of flow of the cooling liquid through the cooling system. A bonuseffect of the lowest possible energy consumption being obtained is thelowest possible noise level of the pump also being obtained. The noiselevel of the pump is amongst other parameters also dependent on thedesign and the rotational speed of the impeller. Thus, an optimisedimpeller design and impeller speed will reduce the noise level to thelowest possible in consideration of ensuring a certain cooling capacity.

BRIEF DESCRIPTION OF THE FIGURES

The invention will hereafter be described with reference to thedrawings, where

FIG. 1 shows an embodiment of the prior art. The figure shows thetypical components in an air-cooling type CPU cooling arrangement.

FIG. 2 shows an embodiment of the prior art. The figure shows the partsof the typical air-cooling type CPU cooling arrangement of FIG. 1 whenassembled.

FIG. 3 shows an embodiment of the prior art. The figure shows thetypical components in a liquid-cooling type CPU cooling arrangement.

FIG. 4 is an exploded view of the invention and the surroundingelements.

FIG. 5 shows the parts shown in the previous figure when assembled andattached to the motherboard of a computer system.

FIG. 6 is an exploded view of the reservoir from the previous FIGS. 4and 5 seen from the opposite site and also showing the pump.

FIG. 7 is a cut-out view into the reservoir housing the pump and aninlet and an outlet extending out of the reservoir.

FIG. 8 is a view of the cooling system showing the reservoir connectedto the heat radiator.

FIG. 9-10 are perspective views of a possible embodiment of reservoirhousing providing direct contact between a CPU and a cooling liquid in areservoir.

FIG. 11-13 are perspective views of a possible embodiment of heat sinkand a reservoir housing constituting an integrated unit.

FIG. 14 is a perspective view of the embodiment shown in FIG. 9-10 andthe embodiment shown in FIG. 11-13 all together constituting anintegrated unit.

FIG. 15-16 are perspective view of a preferred embodiment of a reservoirand a pump and a heat exchanging surface constituting an integratedunit.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an exploded view of an embodiment of prior art coolingapparatus for a computer system. The figure shows the typical componentsin an air-cooling type CPU cooling arrangement. The figure shows a priorart heat sink 4 intended for air cooling and provided with segmentsintersected by interstices, a prior art air fan 5 which is to be mountedon top of the heat sink by use of fastening means 3 and 6.

The fastening means comprises a frame 3 provided with holes intended forbolts, screws, rivets or other suitable fastening means (not shown) forthereby attaching the frame to a motherboard 2 of a CPU 1 or ontoanother processing unit of the computer system. The frame 3 is alsoprovided with mortises provided in perpendicular extending studs in eachcorner of the frame, said mortises intended for taking up tenons of acouple of braces. The braces 6 are intended for enclosing the heat sink4 and the air fan 5 so that the air fan and the heat sink thereby issecured to the frame. Using proper retention mechanisms, when the frameis attached to the motherboard of the CPU of other processing unit, andwhen the tenons of the braces are inserted into the mortises of theframe, the air fan and heat exchanger is pressed towards the CPU byusing a force perpendicular to the CPU surface, said force beingprovided by lever arms.

FIG. 2 shows the parts of the typical air-cooling type CPU coolingarrangement of FIG. 1, when assembled. The parts are attached to eachother and will be mounted on top of a CPU on a motherboard (not shown)of a computer system.

FIG. 3 shows another embodiment of a prior art cooling system. Thefigure shows the typical components in a liquid-cooling type CPU coolingarrangement. The figure shows a prior art heat exchanger 7, which is inconnection with a prior art liquid reservoir 8, a prior art liquid pump9 and a heat radiator 11 and an air fan 10 provided together with theheat radiator. The prior art heat exchanger 7, which can be mounted on aCPU (not shown) is connected to a radiator and reservoir, respectively.The reservoir serves as a storage unit for excess liquid not capable ofbeing contained in the remaining components. The reservoir is alsointended as a means for venting the system of any air entrapped in thesystem and as a means for filling the system with liquid. The heatradiator 11 serves as a means for removing the heat from the liquid bymeans of the air fan 10 blowing air through the heat radiator. All thecomponents are in connection with each other via tubes for conductingthe liquid serving as the cooling medium.

FIG. 4 is an exploded view of a cooling system according to anembodiment of the invention. Also elements not being part of the coolingsystem as such are shown. The figure shows a central processing unit CPU1 mounted on a motherboard of a computer system 2. The figure also showsa part of the existing fastening means, i.e. amongst others the frame 3with mortises provided in the perpendicular extending studs in eachcorner of the frame. The existing fastening means, i.e. the frame 3 andthe braces 6, will during use be attached to the motherboard 2 by meansof bolts, screws, rivets or other suitable fastening means extendingthrough the four holes provided in each corner of the frame andextending through corresponding holes in the motherboard of the CPU. Theframe 3 will still provide an opening for the CPU to enable the CPU toextend through the frame.

The heat exchanging interface 4 is a separate element and is made of aheat conducting material having a relative high heat thermalconductivity such as copper or aluminium, and which will be in thermalcontact with the CPU 1, when the cooling system is fastened to themotherboard 2 of the CPU. The heat exchanging surface constitutes partof a liquid reservoir housing 14, thus the heat exchanger 4 constitutesthe part of the liquid reservoir housing facing the CPU. The reservoirmay as example be made of plastic or of metal. The reservoir or anyother parts of the cooling system, which are possibly manufactured froma plastic material may be “metallised” in order to minimise liquiddiffusion or evaporation of the liquid. The metal may be provided as athin layer of metal coating provided on either or on both of theinternal side or the external side of the plastic part.

If the reservoir is made of metal or any other material having arelative high heat conductivity compared to as example plastic, the heatexchanging interface as a separate element may be excluded because thereservoir itself may constitute a heat exchanger over an area, whereinthe reservoir is in thermal contact with the processing unit.Alternatively to having the heat exchanging interface constitute part ofthe liquid reservoir housing, the liquid reservoir housing may betightly attached to the heat exchanging interface by means of screws,glue, soldering, brazing or the like means for securing the heatexchanging interface to the housing and vice versa, perhaps with asealant 5 provided between the housing and the heat exchanginginterface.

Alternatively to providing a heat exchanging interface integrate withthe reservoir containing the cooling liquid, it will be possible toexclude the heat exchanger and providing another means for dissipatingheat from the processing unit to the cooling liquid in the reservoir,The other means will be a hole provided in the reservoir, said holeintended for being directed towards the processing unit. Boundaries ofthe hole will be sealed towards boundaries of the processing unit orwill be sealed on top of the processing unit for thereby preventingcooling liquid from the reservoir from leaking. The only prerequisite tothe sealing is that a liquid-tight connection is provided betweenboundaries of the hole and the processing unit or surrounding of theprocessing unit, such as a carrier card of the processing unit.

By excluding the heat exchanger, a more effective heat dissipation willbe provided from the processing unit and to the cooling liquid of thereservoir, because the intermediate element of a heat exchanger iseliminated. The only obstacle in this sense is the provision of asealing being fluid-tight in so that the cooling liquid in the reservoiris prevented from leaking.

The heat exchanging surface 4 is normally a copper plate. When excludingthe heat exchanging surface 4, which may be a possibility not only forthe embodiments shown in FIG. 4, but for all the embodiments of theinvention, it may be necessary to provide the CPU with a resistantsurface that will prevent evaporation of the cooling liquid and/or anydamaging effect that the cooling liquid may pose to the CPU. A resistantsurface may be provided the CPU from the CPU producer or it may beapplied afterwards. A resistant surface to be applied afterwards maye.g. be a layer, such as an adhesive tape provided on the CPU. Theadhesive tape may be made with a thin metal layer e.g. in order toprevent evaporation of the cooling liquid and/or any degeneration of theCPU itself.

Within the liquid reservoir, a liquid pump (not shown) is placed forpumping a cooling liquid from an inlet tube 15 connection being attachedto the housing of the reservoir through the reservoir and past the heatexchanger in thermal contact with the CPU to an outlet tube connection16 also being attached to the reservoir housing. The existing fasteningmeans comprising braces 6 with four tenons and the frame 3 with fourcorresponding mortises will fasten the reservoir and the heat exchangerto the motherboard of the CPU. When fastening the two parts of theexisting fastening means to each other the fastening will by means ofthe lever arms 18 create a force to assure thermal contact between theCPU 1 mounted on the motherboard and the heat exchanger 4 being providedfacing the CPU.

The cooling liquid of the cooling system may be any type of coolingliquid such as water, water with additives such as anti-fungicide, waterwith additives for improving heat conducting or other specialcompositions of cooling liquids such as electrically non-conductiveliquids or liquids with lubricant additives or anti-corrosive additives.

FIG. 5 shows the parts shown in FIG. 4 when assembled and attached tothe motherboard of a CPU of a computer system 2. The heat exchanger andthe CPU is in close thermal contact with each other. The heat exchangerand the remainder of the reservoir 14 is fastened to the motherboard 2by means of the existing fastening means being secured to themotherboard of the CPU and by means of the force established by thelever arms 18 of the existing fastening means. The tube inlet connection15 and the tube outlet connection 16 are situated so as to enableconnection of tubes to the connections.

FIG. 6 is an exploded view of the reservoir shown in previous FIG. 4 andFIG. 5 and seen from the opposite site and also showing the pump 21being situated inside the reservoir. Eight screws 22 are provided forattaching the heat exchanging surface 4 to the remainder of thereservoir. The heat exchanging surface is preferably made from a copperplate having a plane outer surface as shown in the figure, said outersurface being intended for abutting the free surface of the heatgenerating component such as the CPU (see FIG. 4). However, also theinner surface (not shown, see FIG. 7) facing the reservoir is plane.Accordingly, the copper plate need no machining other than the shapingof the outer boundaries into the octagonal shape used in the embodimentshown and drilling of holes for insertion of the bolts. No milling ofthe inner and/or the outer surface need be provided.

A sealant in form of a gasket 13 is used for the connection between thereservoir 14 and the heat exchanging surface forming a liquid tightconnection. The pump is intended for being placed within the reservoir.The pump has a pump inlet 20 through which the cooling liquid flows fromthe reservoir and into the pump, and the pump has a pump outlet 19through which the cooling liquid is pumped from the pump and to theoutlet connection. The figure also shows a lid 17 for the reservoir. Thenon-smooth inner walls of the reservoir and the fact that the pump issituated inside the reservoir will provide a swirling of the coolingliquid inside the reservoir.

However, apart from the non-smooth walls of the reservoir and the pumpbeing situated inside the reservoir, the reservoir may be provided withchannels or segments for establishing a certain flow-path for thecooling liquid through the reservoir (see FIG. 9-10 and FIG. 15).Channel or segments are especially needed when the inner surface of theheat exchanging surface is plane and/or when the inner walls of thereservoir are smooth and/or if the pump is not situated inside thereservoir. In either of the circumstances mentioned, the flow of thecooling liquid inside the reservoir may result in the cooling liquidpassing the reservoir too quickly and not being resident in thereservoir for a sufficient amount of time to take up a sufficient amountof heat from the heat exchanging surface. By providing channels orsegments inside the reservoir, a flow will be provided forcing thecooling liquid to pass the heat exchanging surface , and the amount oftime increased of the cooling liquid being resident inside thereservoir, thus enhancing heat dissipation. If channels or segments areto be provided inside the reservoir, the shape and of the channels andsegments may be decisive of whether the reservoir is to be made ofplastic, perhaps by injection moulding, or is to be made of metal suchas aluminium, perhaps by die casting.

The cooling liquid enters the reservoir through the tube inletconnection 15 and enters the pump inlet 20, and is pumped out of thepump outlet 19 connected to the outlet connection 16. The connectionbetween the reservoir and the inlet tube connection and the outlet tubeconnection, respectively, are made liquid tight. The pump may not onlybe a self-contained pumping device, but may be made integrated into thereservoir, thus making the reservoir and a pumping device one singleintegrated component. This single integrated element of the reservoirand the pumping device may also be integrated, thus making thereservoir, the pumping device and the heat exchanging surface one singleintegrated unit. This may as example be possible if the reservoir ismade of a metal such as aluminium. Thus, the choice of material providesthe possibility of constituting both the reservoir and a heat exchangingsurface having a relatively high heat conductivity, and possibly alsorenders the possibility of providing bearings and the likeconstructional elements for a motor and a pumping wheel being part ofthe pumping device. In an alternative embodiment, the pump is placed inimmediate vicinity of the reservoir, however outside the reservoir. Byplacing the pump outside, but in immediate vicinity of the reservoir,still an integrate element may be obtained, The pump or the inlet or theoutlet is preferably positioned so as to obtain a turbulence of flow inthe immediate vicinity of the heat exchanging interface, therebypromoting increased heat dissipation between the heat exchanginginterface end the cooling liquid. Even in the alternative, a pumpingmember such as an impeller (see FIG. 15-16) may be provided in theimmediate vicinity of the heat exchanging surface. The pumping memberitself normally introduces a turbulence of flow, and thereby theincreased heat dissipation is promoted irrespective of the position ofthe pump itself, or the position of the inlet or of the outlet to thereservoir or to the pump.

The pump may be driven by an AC or a DC electrical motor. When driven byan AC electrical motor, although being technically and electricallyunnecessary in a computer system, this may be accomplished by convertingpart of the DC electrical power of the power supply of the computersystem to AC electrical power for the pump. The pump may be driven by anelectrical motor at any voltage common in public electrical networkssuch as 110V or 220V. However, in the embodiment shown, the pump isdriven by a 12V AC electrical motor.

Control of the pump in case the pump is driven by an AC electricalmotor, preferably takes place by means of the operative system or analike means of the computer system itself, and where the computer systemcomprises means for measuring the CPU load and/or the CPU temperature.Using the measurement performed by the operative system or alike systemof the computer system eliminates the need for special means foroperating the pump. Communication between the operative system or alikesystem and a processor for operating the pump may take place alongalready established communication links in the computer system such as aUSB-link. Thereby, a real-time communication between the cooling systemand the operative system is provided without any special means forestablishing the communication. In the case of the motor driving thepump is an AC electrical motor, the above method of controlling the pumpmay be combined with a method, where said pumping means is provided witha means for sensing a position of the rotor of the electrical motor, andwherein the following steps are employed: Initially establishing apreferred rotational direction of the rotor of the electrical motor,before start of the electrical motor, sensing the angular position ofthe rotor, during start, applying an electrical AC voltage to theelectrical motor and selecting the signal value, positive or negative,of the AC voltage at start of the electrical motor, said selection beingmade according to the preferred rotational direction, and saidapplication of the AC voltage being performed by the computer system forapplying the AC voltage from the electrical power supply of the computersystem during conversion of the electrical DC voltage of the powersupply to AC voltage for the electrical motor. By the operative systemof the computer system itself generating the AC voltage for theelectrical motor, the rotational direction of the pump is exclusivelyselected by the computer system, non-depending on the applied voltage ofthe public grid powering the computer system.

Further control strategies utilising the operative system or alikesystem of the computer system may involve balancing the rotational speedof the pump as a function of the cooling capacity needed. If a lowercooling capacity is needed, the rotational speed of the pump, may belimited, thereby limiting the noise generating by the motor driving thepump.

In the case an air fan is provided in combination with a heat sink asshown in FIG. 1, of the air fan is provided in combination with the heatradiator, the operative system or alike system of the computer systemmay be designed for regulating the rotational speed of the pump, andthus of the motor driving the pump, and the rotational speed of the airfan, and thus the motor driving the air fan. The regulation will takeinto account the cooling capacity needed, but the regulation will at thesame time take into account which of the two cooling means, i.e. thepump and the air fan, is generating the most noise. Thus, it the air fangenerally is generating more noise than the pump, then the regulationwill reduce the rotational speed of the air fan before reducing therotational speed of the pump, whenever a lower cooling capacity isneeded. Thereby, the noise level of the entire cooling system is loweredas much as possible. If the opposite is the case, i.e. the pumpgenerally generating more noise than the air fan, then the rotationalspeed of the pump will be reduced before reducing the rotational speedof the air fan. Even further control strategies involve controlling thecooling capacity in dependence on the type of computer processing takingplace. Some kind of computer processing, such as word-processing,applies a smaller load on the processing units such as the CPU thanother kinds of computer processing, such as image processing. Therefore,the kind of processing taking place on the computer system may be usedas an indicator of the cooling capacity. It may even be possible as partof the operative system or similar system to establish certain coolingscenarios, depending on the kind of processing intended by the user. Ifthe user selects as example word-processing, a certain cooling strategyis applied based on a limited need for cooling. If the user selects asexample image-processing, a certain cooling strategy is applied based onan increased need for cooling. Two or more different cooling scenariosmay be established depending on the capacity and the controlpossibilities and capabilities of the cooling system and depending onthe intended use of the computer system, either as selected by a userduring use of the computer system or as selected when choosing hardwareduring build-up of the computer system, i.e. before actual use of thecomputer system.

The pump is not being restricted to a mechanical device, but can be inany form capable of pumping the cooling liquid through the system.However, the pump is preferably one of the following types of mechanicalpumps: Bellows pump, centrifugal pump, diaphragm pump, drum pump,flexible liner pump, flexible impeller pump, gear pump, peristaltictubing pump, piston pump, processing cavity pump, pressure washer pump,rotary lobe pump, rotary vane pump and electro-kinetic pump. Similarly,the motor driving the pumping member need not be electrical but may alsobe a piezo-electrically operated motor, a permanent magnet operatedmotor, a fluid-operated motor or a capacitor-operated motor. The choiceof pump and the choice of motor driving the pump id dependent on manydifferent parameters, and it is up to the person skilled in the art tochoose the type of pump and the type of motor depending on the specificapplication. As example, some pumps and some motors are better suitedfor small computer systems such as lab-tops, some pumps and some motorsare better suited for establishing i high flow of the cooling liquid andthus a high cooling effect, and even some pumps and motors are bettersuited for ensuring a low-noise operation of the cooling system.

FIG. 7 is a cut-out view into the reservoir, when the reservoir and theheat exchanging surface 4 is assembled and the pump 21 is situatedinside the reservoir. The reservoir is provided with the tube inletconnection (not seen from the figure) through which the cooling liquidenters the reservoir. Subsequently, the cooling liquid flows through thereservoir passing the heat exchanging surface and enters the inlet ofthe pump. After having been passed through the pump, the cooling liquidis passed out of the outlet of the pump and further out through the tubeoutlet connection 16. The figure also shows a lid 17 for the reservoir.The flow of the cooling liquid inside the reservoir and trough the pumpmay be further optimised in order to use as little energy as possiblefor pumping the cooling liquid, but still having a sufficient amount ofheat from the heat exchanging surface being dissipated in the coolingliquid. This further optimisation can be established by changing thelength and shape of the tube connection inlet within the reservoir,and/or by changing the position of the pump inlet, and/or for instanceby having the pumping device placed in the vicinity and in immediatethermal contact with the heat exchanging surface and/or by providingchannels or segments inside the reservoir.

In this case, an increased turbulence created by the pumping device isused to improve the exchange of heat between the heat exchanging surfaceand the cooling liquid. Another or an additional way of improving theheat exchange is to force the cooling liquid to pass through speciallyadapted channels or segments being provided inside the reservoir or bymaking the surface of the heat exchanging surface plate inside thereservoir uneven or by adopting a certain shape of a heat sink withsegments. In the figure shown, the inner surface of the heat exchangingsurface facing the reservoir is plane.

FIG. 8 is a perspective view of the cooling system showing the reservoir14 with the heat exchanging surface (not shown) and the pump (not shown)inside the reservoir. The tube inlet connection and the tube outletconnection are connected to a heat radiator by means of connecting tubes24 and 25 through which the cooling liquid flows into and out of thereservoir and the heat radiator, respectively. Within the heat radiator11, the cooling liquid passes a number of channels for radiating theheat, which has been dissipated into the cooling liquid inside thereservoir, and to the surroundings of the heat exchanger. The air fan 10blows air past the channels of the heat radiator in order to cool theradiator and thereby cooling the cooling liquid flowing inside thechannels through the heat radiator and back into the reservoir.According to the invention, the heat radiator 11 may be providedalternatively. The alternative heat radiator is constituted by a heatsink, such as a standard heat sink made of extruded aluminium with finson a first side and a substantially plane second side. An air-fan may beprovided in connection with the fins along the first side. Along thesecond side of the heat sink a reservoir is provided with at least oneaperture intended for being closed by placing said aperture coveringpart of, alternatively covering the whole of, the substantial plane sideof the heat sink. When closing the reservoir in such a way a surface ofthe heat sink is in direct heat exchanging contact with an interior ofthe reservoir, and thus in direct heat exchanging contact with thecooling liquid in the reservoir, through the at least one aperture. Thisalternative way of providing the heat radiator may be used in theembodiment shown in FIG. 8 or may be used as a heat radiator for anotheruse and/or for another embodiment of the invention.

A pumping means for pumping the cooling liquid trough the reservoir mayor may not be provided inside the reservoir at the heat sink. Thereservoir may be provided with channels or segments for establishing acertain flow-path for the cooling liquid through the reservoir. Channelsor segments are especially needed when the inner surface of the heatexchanging surface is plane and/or when the inner walls of the reservoirare smooth and/or if the pump is not situated inside the reservoir. Ineither of the circumstances mentioned, the flow of the cooling liquidinside the reservoir may result in the cooling liquid passing thereservoir too quickly and not being resident in the reservoir for asufficient amount of time to take up a sufficient amount of heat fromthe heat exchanging surface. If channels or segments in the reservoirare to be provided inside the reservoir, the shape and of the channelsand segments may be decisive of whether the reservoir is to be made ofplastic, perhaps by injection moulding, or is to be made of metal suchas aluminium, perhaps by die casting.

By means of the alternative heat radiator, the heat radiator 11 is notprovided as is shown in the figure with the rather expensive structureof channels leading the cooling liquid along ribs connecting thechannels for improved surface of the structure. Instead, the heatradiator is provided as described as a unit constituted by a heat sinkwith or without a fan and a reservoir, and thereby providing a simplerand thereby cheaper heat radiator than the heat radiator 11 shown in thefigure.

The alternative heat radiator provided as an unit constituted by a heatsink and a reservoir, may be used solely, with or without a pump insidethe reservoir and with or without the segments or channels, for beingplaced in direct or indirect thermal contact with a heat generatingprocessing unit such as CPU or with the heat exchanging surface,respectively. These embodiments of the invention may e.g. be used for areservoir, where the cooling liquid along a first side within thereservoir is in direct heat exchanging contact with the heat generatingprocessing unit such as a CPU and the cooling liquid along a second sidewithin the reservoir is in direct heat exchanging contact with a heatsink. Such a reservoir may be formed such as to provide a larger area ofheat exchanging surface towards the heat generating processing unit suchas a CPU than the area of the heat exchanging surface facing the heatsink. This may e.g. have the purpose of enlarging the area of the heatexchanging surface so as to achieve an improved heat dissipation forme.g. the CPU to the heat sink than that of a conventional heat sinkwithout a reservoir attached. Conventional heat sinks normally onlyexchanges heat with the CPU through the area as given by the area of thetop side of the CPU. A system comprising a liquid reservoir and a heatsink with a fan provided has been found to be a simple, cost optimisedsystem with an improved heat dissipation than that of a standard heatsink with a fan, but without the reservoir. In another embodiment of theinvention, which may be derived from FIG. 8, the air fan and the heatradiator is placed directly in alignment of the reservoir. Thereby, thereservoir 14, the air fan 10 and the radiator 11 constitute an integrateunit. Such an embodiment may provide the possibility of omitting theconnection tubes, and passing the cooling liquid directly from the heatradiator to the reservoir via an inlet connection of the reservoir, anddirectly from the reservoir to the heat radiator via an outletconnection of the reservoir. Such an embodiment may even render thepossibility of both the pumping device of the liquid pump inside thereservoir and the electrical motor for the propeller of the air fan 23of the heat radiator 11 being driven by the same electrical motor, thusmaking this electrical motor the only motor of the cooling system. Whenplacing the heat radiator on top of the air fan now placed directly inalignment with the reservoir and connecting the heat radiator directlyto the inlet connection and outlet connection of the reservoir, a needfor tubes will not be present. However, if the heat radiator and thereservoir is not in direct alignment with each other, but tubes maystill be needed, but rather than tubes, pipes made of metal such ascopper or aluminium may be employed, such pipes being impervious to anypossible evaporation of cooling liquid. Also, the connections betweensuch pipes and the heat radiator and the reservoir, respectively, may besoldered so that even the connections are made impervious to evaporationof cooling liquid.

In the derived embodiment just described, an integrated unit of thereservoir, the heat exchanging surface and the pumping device will begiven a structure establishing improved heat radiating characteristicsbecause the flow of air of the air fan may also be directed along outersurfaces of the reservoir. If the reservoir is made of a metal, themetal will be cooled by the air passing the reservoir after havingpassed or before passing the heat radiator. If the reservoir is made ofmetal, and if the reservoir is provided with segments on the outsidesurface of the reservoir, such cooling of the reservoir by the air willbe further improved. Thereby, the integrated unit just described will beapplied improved heat radiating characteristics, the heat radiationfunction normally carried out by the heat radiator thus beingsupplemented by one or more of the further elements of the coolingsystem, i.e. the reservoir, the heat exchanging surface, the liquid pumpand the air fan.

FIG. 9-10 show an embodiment of a reservoir housing 14, where channels25 are provided inside the reservoir for establishing a forced flow ofthe cooling liquid inside the reservoir. The channels 25 in thereservoir 14 lead from an inlet 15 to an outlet 16 like a maze betweenthe inlet and the outlet. The reservoir 14 is provided with an aperture27 having outer dimensions corresponding to the dimensions of a freesurface of the processing unit 1 to be cooled. In the embodiment shown,the processing unit to be cooled is a CPU 1.

When channels 26 are provided inside the reservoir, the shape of thechannels may be decisive of whether the reservoir is to be made ofplastic, perhaps manufactured by injection moulding, or is to be made ofmetal such as aluminium, perhaps manufactured by extrusion or by diecasting.

The reservoir 14 or any other parts of the cooling system, which arepossibly manufactured from a plastic material may be “metallised” inorder to minimise liquid diffusion or evaporation of the liquid. Themetal may be provided as a thin layer of metal coating provided oneither or on both of the internal side or the external side of theplastic part. The CPU 1 is intended for being positioned in the aperture27, as shown in FIG. 10, so that outer boundaries of the CPU areengaging boundaries of the aperture. Possibly, a sealant (not shown) maybe provided along the boundaries of the CPU and the aperture forensuring a fluid tight engagement between the boundaries of the CPU andthe boundaries of the aperture. When the CPU 1 is positioned in theaperture 27, the free surface (not shown) of the CPU is facing thereservoir, i.e. the part of the reservoir having the channels provided.Thus, when positioned in the aperture 27 (see FIG. 10), the free surfaceof the CPU 1 is having direct contact with cooling liquid flowingthrough the channels 26 in the reservoir.

When cooling liquid is forced from the inlet 15 along the channels 26 tothe outlet 16, the whole of the free surface of the CPU 1 will be passedover by the cooling liquid, thus ensuring a proper and maximised coolingof the CPU. The configuration of the channels may be designed andselected according to any one or more provisions, i.e. high heatdissipation, certain flow characteristics, ease of manufacturing etc.Accordingly, the channels may have another design depending on anydesire or requirement and depending on the type of CPU and the size andshape of the free surface of the CPU. Also. other processing units thana CPU may exhibit different needs for heat dissipation, and may exhibitother sizes and shapes of the free surface, leading to a need for otherconfigurations of the channels. If the processing unit is very elongate,such as a row of microprocessors, one or a plurality of parallelchannels may be provided, perhaps just having a common inlet and acommon outlet.

FIG. 11-13 show an embodiment of a heat sink 4, where segments 28 areprovided at a first side 4A of the heat sink, and fins 29 fordissipating heat to the surroundings are provided at the other, secondside 4B of the heat sink. An intermediate reservoir housing 30 isprovided having a recessed reservoir at the one side facing the firstside 4A of the heat sink. The recessed reservoir 30 has an inlet 31 andan outlet 32 at the other side opposite the side facing the heat sink 4.

When segments 28 are provided on the first side 4A of the heat sink, theshape of the segments may be decisive of whether the reservoir, which ismade from metal such as aluminium or copper, is to be made by extrusionor is to be made by other manufacturing processes such as die casting.Especially when the segments 28 are linear and are parallel with thefins 29, as shown in the embodiment, extrusion is a possible andcost-effective means of manufacturing the heat sink 4.

The intermediate reservoir 30 or any other parts of the cooling system,which are possibly manufactured from a plastic material may be“metallised” in order to minimise liquid diffusion or evaporation of theliquid. The metal may be provided as a thin layer of metal coatingprovided on either or on both of the internal side or the external sideof the plastic part. The recessed reservoir is provided with a kind ofserration 33 along opposite sides of the reservoir, and the inlet 31 andthe outlet 32, respectively, are provided at opposite corners of theintermediate reservoir 30. The segments 28 provided at the first side 4Aof the heat sink, i.e. the side facing the intermediate reservoir 30,are placed so that when the heat sink is assembled with the intermediatereservoir housing (see FIG. 13) the segments 29 run from one serratedside of the reservoir to the other serrated side of the reservoir.

When cooling liquid is forced from the inlet 31 through the reservoir,along channels (not shown) formed by the segments 29 of the heat sink 4and to the outlet 32, the whole of the first side 4A of the heat sinkwill be passed over by the cooling liquid, thus ensuring a proper andmaximised heat dissipation between the cooling liquid and the heat sink.The configuration of the segments on the first side 4A of the heat sinkand the configuration of the serrated sides of the intermediatereservoir housing may be designed and selected according to anyprovisions. Accordingly, the segments may have another design, perhapsbeing wave-shaped or also a serrated shape, depending on any desiredflow characteristics of the cooling liquid and depending on the type ofheat sink and the size and shape of the reservoir.

Also other types of heat sinks, perhaps circular shaped heat sinks mayexhibit different needs for heat dissipation, may exhibit other sizesand shapes of the free surface, leading to a need for otherconfigurations of the segments and the intermediate reservoir. If theheat sink and the reservoir are circular or oval, a spiral-shapedsegmentation or radially extending segments may be provided, perhapshaving the inlet or the outlet in the centre of the reservoir. If animpeller of the pump is provided, as shown in FIG. 15-16, the impellerof the pump may be positioned in the centre of a spiral-shapedsegmentation or in the centre of radially extending segments.

FIG. 14 shows the reservoir 14 shown in FIG. 9-10 and the heat sink 4and the intermediate reservoir 30 shown in FIG. 11-13 being assembledfor thereby constituting an integrated monolithic unit. It is notabsolutely necessary to assemble the reservoir 14 of FIG. 9-10 and theheat sink 4 and the intermediate reservoir 30 of FIG. 11-13 in order toobtain a properly functioning cooling system. The inlet 15 and theoutlet 16 of the reservoir 14 of FIG. 9-10 may be connected to theoutlet 32 and the inlet 31, respectively, of the intermediate reservoirof FIG. 11-13 by means of tubes or pipes.

The reservoir 14 of FIG. 9-10 and the heat sink 4 and the intermediatereservoir 30 of FIG. 11-13 may then be positioned in the computer systemat different locations. However, by assembling the reservoir 14 of FIG.9-10 and the heat sink 4 and the intermediate reservoir 30 of FIG. 11-13a very compact monolithic unit is obtained, also obviating the need fortubes or pipes. Tubes or pipes may involve an increased risk of leakageof cooling liquid or may require soldering or other special working inorder to eliminate the risk of leakage of cooling liquid. By eliminatingthe need for tubes or pipes, any leakage and any additional working isobviated when assembling the cooling system.

FIG. 15-16 show a possible embodiment of a reservoir according to theinvention. The reservoir is basically similar to the reservoir shown inFIG. 9-10. However, an impeller 33 of the pump of the cooling system isprovided in direct communication with the channels 26. Also, in theembodiment shown, a heat exchanging interface 4 such as a surface madefrom a copper plate, alternatively a plate of another material having ahigh thermal conductivity, is placed between the channels 26 inside thereservoir and the CPU 1 as the processing unit.

The heat exchanging surface 4 is preferably made from a copper platehaving a plane outer surface as shown in the figure, said outer surfacebeing intended for abutting the free surface of the heat generatingcomponent such as the CPU 1 (see FIG. 4). However, also the innersurface (not shown, see FIG. 7) facing the reservoir is plane.Accordingly, the copper plate need no machining other than the shapingof the outer boundaries into the specially adapted shape used in theembodiment shown and drilling of holes for insertion of the bolts. Nomilling of the inner and/or the outer surface need be provided.

The provision of the heat exchanging surface 4 need not be a preferredembodiment, seeing that the solution incorporating the aperture (seeFIG. 9-10) result in a direct heat exchange between the free surface ofthe CPU or other processing unit and the cooling liquid flowing alongthe channels in the reservoir. However, the heat exchanging surfaceenables usage of the cooling system independently on the type and sizeof the free surface of CPU or other processing unit.

In the embodiment shown, the heat exchanging surface 4 is secured to thereservoir by means of bolts 22. Other convenient fastening means may beused. The heat exchanging surface 4 and thus the reservoir 14 may befastened to the CPU 1 or other processing unit by any suitable meanssuch as soldering, brazing or by means of thermal paste combined withglue. Alternatively, special means (not shown) may be provided forensuring a thermal contact between the free surface of the CPU or otherprocessing unit and the heat exchanging surface. One such means may bethe fastening means shown in FIG. 4 and FIG. 5 or similar fasteningmeans already provided as part of the computer system.

When channels 26 are provided inside the reservoir 14, the shape of thechannels may be decisive of whether the reservoir is to be made ofplastic, perhaps by injection moulding, or is to be made of metal suchas aluminium, perhaps by die casting.

The reservoir 14 or any other parts of the cooling system, which arepossibly manufactured from a plastic material may be “metallised” inorder to minimise liquid diffusion or evaporation of the liquid. Themetal may be provided as a thin layer of metal coating provided oneither or on both of the internal side or the external side of theplastic part. The impeller 33 (see FIG. 14) of the pump is positioned ina separate recess of the channels 26, said separate recess having a sizecorresponding to the diameter of the impeller of the pump. The recess isprovided with an inlet 34 and an outlet 35 being positioned opposite aninlet 31 and an outlet 32 of cooling liquid to and from, respectively,the channels 26. The impeller 33 of the pump has a shape and a designintended only for one way rotation, in the embodiment shown a clock-wiserotation only. Thereby, the efficiency of the impeller of the pump ishighly increased compared to impellers capable of and intended for bothclock-wise and counter clock-wise rotation.

The increased efficiency of the impeller design results in the electricmotor (not shown) driving the impeller of the pump possibly beingsmaller than otherwise needed for establishing a proper and sufficientflow of cooling liquid through the channels. In a preferred embodiment,the electric motor is an AC motor, preferably a 12V AC motor, leading tothe possibility of an even smaller motor needed for establishing theproper and sufficient flow of cooling liquid through the channels.

The impeller of the pump may be driven by an AC or a DC electricalmotor. However, as mentioned, preferably the impeller of the pump isdriven by an AC electrical motor. Although being technically andelectrically unnecessary to use an AC electrical motor in a computersystem, this may be accomplished by converting part of the DC electricalpower of the power supply of the computer system to AC electrical powerfor the impeller of the pump. The impeller may be driven by anelectrical motor at any voltage common in public electrical networkssuch as 110V or 220V. However, in the embodiment shown, the impeller ofthe pump is driven by a 12V electrical motor.

The invention has been described with reference to specific embodimentsand with reference to specific utilisation, it is to be noted that thedifferent embodiments of the invention may be manufactured, marketed,sold and used separately or jointly in any combination of the pluralityof embodiments. In the above detailed description of the invention, thedescription of one embodiment, perhaps with reference to one or morefigures, may be incorporated into the description of another embodiment,perhaps with reference to another or more other figures, and vice versa.Accordingly, any separate embodiment described in the text and/or in thedrawings, or any combination of two or more embodiments is envisaged bythe present application.

1-19. (canceled)
 20. A cooling system for a computer system processingunit, comprising: a reservoir configured to circulate a cooling liquidtherethrough, the reservoir including: an upper chamber and a lowerchamber, wherein the upper chamber and the lower chamber are verticallydisplaced separate fluid-containing receptacles that are each surroundedby boundary walls, wherein at least one of the boundary walls separatethe upper chamber from the lower chamber; channels provided in thereservoir for establishing a certain flow path for the cooling liquid;an inlet that fluidly couples the lower chamber to the upper chamber,wherein the inlet is positioned between a first end and a second end ofthe lower chamber; an outlet positioned at one of the first end orsecond end of the lower chamber wherein the cooling liquid is directedfrom the lower chamber; wherein the lower chamber includes a pluralityof parallel channels configured to split the flow of cooling liquid anddirect the cooling liquid from the central region toward the perimeterof the lower chamber where the cooling liquid is collected along theperimeter and directed from the lower chamber through the outlet; a heatexchanging interface attached to the reservoir to form a boundary wallof the lower chamber, the heat exchanging interface provides thermalcontact between the processing unit and the cooling liquid; a pumphaving an electrically operated rotary motor and rotor having animpeller, the pump having at least one sensor for sensing a position ofthe rotor; and a radiator spaced apart from and fluidly coupled to thereservoir.
 21. The cooling system of claim 20, further including acontrol system, wherein the control system is configured to adjust aspeed of the pump.
 22. The cooling system of claim 20, wherein thecontrol system is part of an operating system of the computer.
 23. Thecooling system of claim 22, wherein the control system is configured tomeasure one of an operating load or an operating temperature of theprocessing unit and adjust the pump based on the measured value.
 24. Thecooling system of claim 22, wherein the control system is configured todetermine a required cooling capacity of the cooling system and adjust arotational speed of the pump based on the required cooling capacity. 25.The cooling system of claim 22, wherein the control system is configuredto reduce the rotational speed of the pump if lower cooling capacity isrequired.
 26. The cooling system of claim 20, wherein the impeller isconfigured to optimize the rotational speed necessary for obtaining apredetermined flow of cooling liquid through the cooling system.
 27. Thecooling system of claim 20, wherein the heat exchange interface is heldin thermal contact with a free surface of a CPU on a motherboard of acomputer system.
 28. The cooling system of claim 20, wherein coolingliquid passes directly from the heat radiator to the reservoir via aninlet connection to the reservoir, and directly from the reservoir tothe heat radiator via an outlet connection of the reservoir.
 29. Thecooling system of claim 27 configured such that the whole of the freesurface of the CPU is passed over by the cooling liquid on the heatexchange interface.